The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The metal heat treatment industry has many heat treatment methods and processes available for many specific purposes related to various metal products. Heat treatment methods include processes to case harden, strengthen, temper, provide corrosion resistance, stress relieve, coat, etch, as well as many others.
Metal products are commonly fully machined prior to introduction to the heat treatment process. The various heat treatment processes harden the metal and/or stress relieve it, and/or coat it, and/or provide a secondary function of surface treatment or corrosion resistance.
Other metal products are formed prior to heat treatment by one or more manufacturing processes such as stamping, bending, rolling, forging, drawing, winding, etcetera. Subsequent heat treatment provides any one or a combination of the benefits of heat treatment mentioned previously.
Each of these metal-forming processes requires the metal to be yielded in order to shape it. This is true of machining processes that must yield the metal away as it is cut. It is also true of forming processes that must cause the metal to yield into a new shape as it is bent, such as a wound spring or a stamping or bent mounting bracket.
One specialized forming process uses heat treatment to yield and subsequently form the metal product. A windshield wiper beam is the subject of U.S. Pat. No. 6,622,540 which discloses a process of exposing one side of a wiper beam to a heat source while maintaining a cooler temperature on the opposite side of the beam. This process causes the heated surface of the beam to thermally expand greater than the opposing unheated surface of the beam. As a result, the beam is thermally curved.
Excluding the '540 patent, all methods mentioned above require the use of some hard tooling to form yield metal products prior to heat treatment. The tooling is expensive to build and maintain and requires the cost and time of a manufacturing step or sequence of manufacturing steps to yield and form the metal product.
The '540 patent overcomes the disadvantages of traditional forming processes by eliminating the need for hard tooling and the manufacturing step(s) normally associated therewith. However, the '540 patent adds the disadvantage of a specialized heat source process that is difficult to thermally control, and thus difficult to manufacture precise repeatable arc forms. Heat travels through materials at different rates based on the thermal diffusivity of the material. The '540 patent applies heat to one side of a thin metal backbone of a beam wiper and begins to thermally expand that side while maintaining a significantly lower thermal expansion on the opposite side of the thin metal beam. Thermal diffusivity of a thin metal beam is high, resulting in a rapid transfer of heat conduction through the thin metal beam. Therefore, a significant delta-T and a corresponding significant difference of thermal expansion will be unlikely, not to mention difficult and impractical to control.